This invention relates to a process of preparing 2,2-bis(4-aminophenyl)hexafluoropropane which is a compound useful as the material of some fluororesins such as fluorine-containing polyimides.
U.S. Pat. No. 4,370,501 shows preparing 2,2-bis(4-aminophenyl)hexafluoropropane by the steps of converting potassium salt of 2,2-bis(4-hydroxyphenyl)hexafluoropropane into a 4-chloro-2-phenylquinazoline in dimethylsufoxide and isolateing the quinazoline, converting the quinazoline into a bisquinazolinone by heating at about 320.degree. C. and hydrolyzing the quinazolinone to thereby obtain the aimed compound. However, this process is not suitable for industrial practice because of using expensive reagents and including reactions which must be carried out under severe conditions.
Zh. Vses. Khin. Obshchestva im. D. I. Mendeleeva, 11(4), 469(1966) shows that 2,2-bis(4-aminophenyl)hexafluoropropane is obtained from 2,2-bis(4-methylphenyl)hexafluoropropane, which can be prepared relatively easily, by the steps of oxidizing the starting compound by dilute nitric acid to obtain a corresponding carboxylic acid, converting the obtained acid into an acid chloride by reaction with thionyl chloride, mixing an acetone solution of the acid chloride with an aqueous solution of sodium azide to precipitate an acid azide and recovering it by filtration, heating the acid azide in xylene to cause rearrangement into an isocyanate and distilling the reaction liquid to isolate the isocyanate and hydrolyzing the isocyanate by hydrochloric acid to thereby obtain the aimed diamine. However, this process is unfavorable for industrial practice because of having many steps, including troublesome operations for separating solid intermediates and needing isolation of the intermediately formed isocyanate, which has a high boiling point, by distiallation.
U.S. Pat. No. 3,310,573 shows preparing 2,2-bis(4-aminophenyl)hexafluoropropane by the steps of oxidizing 2,2-bis(4-methylphenyl)hexafluoropropane in acetic acid by chromium trioxide to obtain a corresponding carboxylic acid, suspending the carboxylic acid in a mixture of sulfuric acid and chloroform and adding hydrogen azide to the suspension to thereby convert the carboxylic acid into an acid azide, heating the acid azide to form an isocyanate as an intermediate and then obtain sulfate of the aimed diamine. This process consists of a relatively small number of steps, but it is a disadvantage to use a large amount of hydrogen azide which is instable and highly toxic.